1. Technical Field
The present disclosure relates to a system for the measure of the strain of an object. Still more in particular, the disclosure concerns a strain measurement system based on the strain of an optical fiber.
2. Description of the Related Art
It is known that the measure of the strain of an object can be performed by a system including a laser source and an optical fiber: this measurement system is commonly indicated as strain measurement system (or strain sensor) based on the optical fiber (or shortly as “fiber based strain system”).
A known fiber based strain system (see for example the US application having publication number 2008/0085073) performs the measure of the object strain using an optical fiber including a fiber Bragg grating in a short segment (few centimeters long) of the optical fiber which is attached to the strainable object and it's strained thereof. According to the known system, the laser source generates an output radiation, which is guided over the optical fiber and it's reflected by the fiber Bragg grating, wherein the reflected radiation is affected by a wavelength shift which depends on the strain of the segment of the optical fiber including the fiber Bragg grating. A receiver converts the reflected radiation into electrical signals and a spectrum analyzer estimates the strain of the segment of the optical fiber (including the fiber Bragg grating) from the variation of the amplitude of the reflected radiation. This known system has the disadvantages that the resolution of the strain measure depends on the stop-band of the fiber Bragg grating, that complex electronic devices are required for performing the measure and that it's possible to perform the measure of only a short segment of the strainable object (for example, a structural joint) because the fiber Bragg grating is few centimeters long.
Another known fiber based strain system (see for example the European application having publication number EP1760424) performs the measure of the object strain using the Brillouin scattering phenomenon, by determining the Brillouin loss or gain spectrum from the light emerging from the optical fiber. This known system has the disadvantages to require an expensive optical fiber (Erbium doped), to require an high power laser source and to require complex electronic devices for performing the measure.